A finger follower lever is a transmission element in a valve train (e.g., that of a piston-type internal combustion engine) via which the lifting movement of a cam brought about by the rotation of a camshaft is transmitted to a lift valve, which is opened axially against the restoring three of a valve spring in order to change the charge. For this purpose, the finger follower lever is supported in an articulated manner at one end on a housing-side supporting element and, at the opposite end, rests against the stem end of the associated lift valve. Between its ends, the finger follower lever is in contact, on the side thereof facing away from the supporting element and the lift valve, with the associated cam of the camshaft so that the lift specified by the contour of the cam can be transmitted to the stem end of the lift valve with an increase corresponding to the effective leverage. To obtain a valve train with as little friction as possible, the finger follower lever is often designed as a so-called roller finger follower lever (i.e., is provided with a rotatably mounted roller which is in contact with the associated cam of the camshaft).
In the present case, the starting point is a finger follower lever. The lever body of the finger follower is a pressed and punched component made of sheet metal that has a U-shaped cross section with two largely parallel side walls. Arranged between the side walls is a roller rotatably mounted on a pin. The pin is inserted at each end into a hole punched out of the side wall and is staked or caulked at the ends. In contrast to a lever body which is produced as a casting, which entails involved mechanical finish machining, this type has the advantage that it can be produced especially economically and, at the same time, accurately in mass production. A corresponding finger follower lever, which is provided at the valve-side end thereof with two guide checks for lateral guidance on the stem end of the lift valve, and a method for the production thereof are known, for example, from DE 100 30 341 C2.
In the production of the finger follower lever, the holes for accommodating the pin are preferably punched out of the side walls simultaneously and in opposite directions after the forming of the body of the finger follower lever. For this purpose, the lever body is placed in a punching tool, in which the insides of the two side walls rest against a punching tool die provided with an oversized hole and the holes are punched out simultaneously from the outside inward by two punching tool punches moved toward one another. During this process, the punched-out sheet-metal segments are pressed into the die so that the lever body can then be removed from the punching tool. This production method gives the best possible coaxial alignment between the two holes but cannot be employed without additional measures unless the inner spacing between the two side walls is greater than twice the wall thickness of the side walls.
While this condition is generally satisfied in the case of finger follower levers for simple valve trains, variable valve trains with sliding cam systems, like the known “Audi Valve Lift System (AVS)” and the known sliding cam system made by Schaeffler GmbH & Co. KG require relatively narrow finger follower levers where this condition cannot be satisfied because of restricted space conditions. In order to enable the holes nevertheless to be punched out simultaneously in opposite directions in this case, DE 10 2004 012 142 A1 proposes to provide a conical taper on the side walls in the region of the holes and, thus, to reduce the thickness of the sheet-metal segments punched out, However, since a defined chamfer to partially accommodate the pin material displaced radially during staking or caulking is required in any case when using pins with soft ends which are massively staked or caulked after insertion, the conical taper on the side walls must be centered accurately relative to the holes. During production of the conical taper on the side walls by stamping, raised portions are furthermore produced at the transition to the cylindrical holes, leading to increased pin contact pressure in the holes.
As described in DE 10 2009 032 143 A1, studies carried out by the applicant have now shown that uniformly through-hardened pins can also be used in such applications. Through-hardened pins can be produced more economically, do not require any chamfer on the outer edge of the respective hole and can be expanded radially by a sufficient amount for positive axial retention at the ends thereof by a single application of axial force using a staking or caulking bell with a concave shape in the area of contact.